Inkjet printing

ABSTRACT

The present disclosure relates to an inkjet printing process that comprises applying a radiation-curable primer composition onto a substrate to form a primer layer. The primer composition comprises a curable polyurethane dispersion, a photoinitiator and water. An inkjet ink composition is inkjet printed onto the primer layer as a printed inkjet ink layer. The inkjet ink composition comprises a colorant, a curable polyurethane dispersion, a photoinitiator and water. The curable polyurethane is dispersed in the inkjet ink composition in an amount of composition is 0.1 to 30 weight % of the inkjet ink composition. The printed inkjet ink layer is cured on the substrate by exposing both the primer layer and printed inkjet ink layer on the substrate to radiation.

BACKGROUND

Inkjet printing is a printing method that utilizes electronic signals tocontrol and direct droplets or a stream of ink onto print media. Inkjetprinting may involve forcing ink drops through small nozzles by thermalejection, piezoelectric pressure or oscillation onto the surface of themedia. This technology can be used to record images on various mediasurfaces (e.g. paper).

In inkjet printing, curable polymer binders may be added to inkjet inksto improve the durability of the resulting print. Such binders may becured, for example, by exposure to radiation e.g. UV radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

Various implementations are described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating, by way of example, anexample of a printing process of the present disclosure.

DETAILED DESCRIPTION

Before the present disclosure is disclosed and described, it is to beunderstood that this disclosure is not limited to the particular processsteps and materials disclosed in this disclosure because such processsteps and materials may vary. It is also to be understood that theterminology used in this disclosure is used for the purpose ofdescribing particular examples. The terms are not intended to belimiting because the scope is intended to be limited by the appendedclaims and equivalents thereof.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used in this disclosure, “primer” in the context of the presentdisclosure refers to a composition that is applied to a print substrateas an under layer to the inkjet ink composition. The primer compositionmay be substantially colourless, clear or transparent. Accordingly, theprimer composition may be substantially free from pigment or othercolorants, and may have no substantive effect on the colour of anoverprinted coloured image printed from inkjet ink.

As used in this disclosure, “acidity,” “acid number,” or “acid value”refers to the mass of potassium hydroxide (KOH) in milligrams thatneutralizes one gram of a substance. The acidity of a polymer can bemeasured according to standard techniques, for example as described inASTM D1386. If the acidity of a particular polymer is specified, unlessotherwise stated, it is the acidity for that polymer alone, in theabsence of any of the other components of the primer or inkjet inkcomposition.

Optical density or absorbance is a quantitative measure expressed as alogarithmic ratio between the radiation falling upon a material and theradiation transmitted through a material.

${A_{\lambda} = {- {\log_{10}\left( \frac{I_{1}}{I_{0}} \right)}}},$where A_(λ) is the absorbance at a certain wavelength of light (λ), I₁is the intensity of the radiation (light) that has passed through thematerial (transmitted radiation), and I₀ is the intensity of theradiation before it passes through the material (incident radiation).The incident radiation may be any suitable white light, for example, daylight or artificial white light. The optical density or delta E of animage may be determined using methods that are well-known in the art.For example, optical density and/or delta E may be determined using aspectrophotometer. Suitable spectrophotometers are available under thetrademark X-rite.

As used in this disclosure, the term “about” is used to provideflexibility to a numerical range endpoint by providing that a givenvalue may be a little above or a little below the endpoint to allow forvariation in test methods or apparatus. The degree of flexibility ofthis term can be dictated by the particular variable and would be withinthe knowledge of those skilled in the art to determine based onexperience and the associated description in this disclosure.

As used in this disclosure, a plurality of items, structural elements,compositional elements, and/or materials may be presented in a commonlist for convenience. However, these lists should be construed as thougheach member of the list is individually identified as a separate andunique member. Thus, no individual member of such list should beconstrued as a de facto equivalent of any other member of the same listsolely based on their presentation in a common group without indicationsto the contrary.

Concentrations, amounts, and other numerical data may be expressed orpresented in this disclosure in a range format. It is to be understoodthat such a range format is used merely for convenience and brevity andthus should be interpreted flexibly to include not just the numericalvalues explicitly recited as the limits of the range, but also toinclude all the individual numerical values or sub-ranges encompassedwithin that range as if each numerical value and sub-range is explicitlyrecited. As an illustration, a numerical range of “about 1 wt % to about5 wt %” should be interpreted to include not just the explicitly recitedvalues of about 1 wt % to about 5 wt %, but also include individualvalues and subranges within the indicated range. Thus, included in thisnumerical range are individual values such as 2, 3.5, and 4 andsub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This sameprinciple applies to ranges reciting a single numerical value.Furthermore, such an interpretation should apply regardless of thebreadth of the range or the characteristics being described.

The present disclosure relates to an inkjet printing process thatcomprises applying a radiation-curable primer composition onto asubstrate to form a primer layer. The primer composition comprises acurable polyurethane dispersion, a photoinitiator and water. An inkjetink composition is inkjet printed onto the primer layer as a printedinkjet ink layer. The inkjet ink composition comprises a colorant, acurable polyurethane dispersion, a photoinitiator and water. The curablepolyurethane is dispersed in the inkjet ink composition in an amount ofcomposition is 0.1 to 30 weight % of the inkjet ink composition. Theprinted inkjet ink layer is cured on the substrate by exposing both theprimer layer and printed inkjet ink layer on the substrate to radiation.

The present disclosure also relates to a printed substrate comprising aprimer layer disposed over the substrate and an ink layer comprising acolorant disposed over the primer layer, wherein the printed substratecomprises a crosslinked polyurethane network that surrounds the colorantand extends from the primer layer to the ink layer.

Polyurethane dispersions may be used as curable polymer binders inaqueous UV-curable inkjet ink compositions. However, it can be difficultto achieve adequate durability without compromising othercharacteristics of the inkjet ink composition. For example, while highlevels of polymer binder can improve durability, excessive levels ofpolymer binder can affect the jettability of the inkjet ink composition.The latter can have a negative effect on the printed image, as well ason the lifespan of the printhead. Moreover, aqueous UV-curable inkscomprising e.g. yellow or black colorants may be difficult to curebecause these colorants may be strong absorbers of UV light. Whilecuring may be improved by increasing the polyurethane and/orphotoinitiator content of the inkjet ink, this may have a detrimentaleffect on the jettability of the ink composition.

In the present disclosure, a polyurethane dispersion is included in aprimer composition that is applied as an underlayer to the inkjet inkcomposition. This can allow higher levels of polyurethane to bedeposited onto the substrate to enhance durability. At the same time,the polyurethane content of the inkjet ink composition can be kept belowa threshold to maintain desired levels of jettability. The relativeconcentrations of polyurethane in the primer composition and inkjet inkcomposition may be tailored to provide the desired levels of durability,while maintaining jettability of the inkjet ink compositions and, in thecase of a digital primer, also the jettability of the primercomposition.

In some examples, the primer composition may be applied in an analoguemanner, for example, by coating. Since the primer composition need notbe applied digitally using a printhead, high levels of polyurethane canbe employed without the risk of compromising jettability.

Furthermore, in the present disclosure, both the primer composition andthe inkjet ink composition comprise curable polyurethane. Thus, when theprimer and the inkjet ink are exposed to radiation, photoinitiators inthe primer and inkjet ink generate reactive species e.g. radicals. Thesereactive species react to cure the polyurethane in the primer and inkjetink, forming a crosslinked polyurethane network that extends from theprimer layer to the inkjet ink layer. This crosslinked polyurethanenetwork can help to retain pigment on the substrate, improving thedurability of the printed image on the substrate. In some examples,reactive groups of the polyurethane in the primer layer crosslink withreactive groups of the polyurethane in the ink layer. In some examples,the crosslinked polyurethane network may surround the colorant in theink layer.

Primer

The primer composition comprises water, a photoinitiator and a curablepolyurethane dispersion. The primer composition may additionallycomprise a surfactant.

Water may be present in the primer composition in an amount of at least30 weight %, for example, at least 40 or 50 weight %. In some examples,water may be present in the primer composition in an amount of at least60 weight %. Water may be present in an amount of at most 99 weight %,for example, at most 95 weight %. In some examples, water may be presentin the primer composition in an amount of 30 to 99 weight %, forinstance, 40 to 98 weight % or 50 to 95 weight %. In other examples,water may be present in an amount of 60 to 93 weight %, for instance, 70to 90 weight %.

Any suitable photoinitiator may be employed in the primer composition.The photoinitiator initiates the polymerization and/or crosslinking ofthe radiation-curable polyurethane upon exposure to radiation. Thephotoinitiator may be the same or different from the photoinitiatoremployed in the inkjet ink composition. Suitable photoinitiators aredescribed in relation to the primer composition below. However, for theavoidance of doubt, the water-soluble photoinitiators described inrelation to the inkjet ink composition may be used in the primercomposition, if desired.

Some examples of the photoinitiator include1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (whichis commercially available from BASF Corp. as IRGACURE® 2959); acylphosphine oxide photoinitiators (e.g., IRGACURE® 819, commerciallyavailable from BASF Corp.); alpha hydroxy ketone photoinitiators (e.g.,IRGACURE® 184, commercially available from BASF Corp.); Iodonium,(4-methylphenyl)[4-(2-methylpropyl) phenyl]-, hexafluorophosphate(I—)(which is commercially available from BASF Corp. as IRGACURE® 250); ahigh-molecular-weight sulfonium salt (e.g., IRGACURE® 270, commerciallyavailable from BASF Corp.);2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (which iscommercially available from BASF Corp. as IRGACURE® 369); alpha aminoketone photoinitiator (e.g., IRGACURE® 379, commercially available fromBASF Corp.); a liquid blend of alpha hydroxy ketone/benzophenonephotoinitiator (e.g., IRGACURE® 500, commercially available from BASFCorp.); and a liquid photoinitiator blend of acyl phosphine oxide/alphahydroxy ketone (e.g., IRGACURE® 2022, commercially available from BASFCorp.). Some other suitable photoinitiators include phosphine oxidederivatives, thioxanthone derivatives, and benzophenone derivatives.

The photoinitiator may be present in the primer composition in an amountranging from about 0.1 wt % to about 20 wt. % of the total wt % of theprimer composition. In another example, the photoinitiator is present inthe in the inkjet ink in an amount ranging from about 0.2 wt % to about15 wt %, for example, 0.5 wt % to 10 wt % or 0.5 to 5 wt % of the totalwt % of the primer composition.

Any suitable curable polyurethane dispersion may be included in theprimer composition. The polyurethane dispersion may be UV-curable, forexample, curable by UV-LED. Suitable UV-LED wavelengths include 365 nm,385 nm, 395 nm or 405 nm. In one example, the polyurethane dispersionmay be curable by UV-LED at 365 nm, 385 nm or 395 nm. In one example,the polyurethane dispersion may be curable by UV-LED at 395 nm.

The polyurethane may be the same as or different from the polyurethanepresent in the inkjet ink composition. Suitable polyurethanes aredescribed in relation to the primer composition below. However, for theavoidance of doubt, the pH stable polyurethane dispersions describedbelow in relation to the inkjet ink composition may be used to form theprimer composition, if desired.

In some examples, polyurethane dispersions comprise polyurethane polymerparticles dispersed in water. The particles may range from about 20 toabout 200 nm in size. The polyurethane can have a molecular weight (Mw)in the range of about 1,000 to 100,000 or in the range of about 5,000 toabout 50,000. The polyurethane may have a NCO/OH ratio of 1.2 to 5 andan acid number of 20 to 100. The double bond density of the polyurethanemay be 1.5 to 20, for example, 2 to 10.

The polyurethane may be formed from the reaction of a diisocyanate and apolyol. The diisocyanate can be an aliphatic diisocyanate or an aromaticdiisocyanate. Examples of suitable diisocyanates include methylenediphenyl diisocyanate, hexamethylene diisocyanate, p-tetramethyl xylenediisocyanate, m-tetramethyl xylene diisocyanate, bitolylenediisocyanate, toluene diisocyanate,methylene-bis(4-cyclohexyl)diisocyanate, p-phenylene diisocyanate,isophorone diisocyanate, 1,5-naphthalene diisocyanate and mixturesthereof.

In some examples, the polyol can be a diol selected from the group of:cyclic diols (e.g. 1,3-cyclohexanedimethanol and1,4-cyclohexanedimethanol); aliphatic polycarbonate diols; polyetherdiols; polyethylene glycol; polypropylene glycol; polytetramethyleneglycol; poly(ethylene oxide) polymers; poly(propylene oxide) polymers;poly(tetramethylene oxide) polymers; copolymers thereof having terminalhydroxyl groups derived from polyhydric compounds including diols; andcombinations thereof. In one aspect, the diol can be a cyclic diol. Inanother aspect, the diol can be an aliphatic cyclic diol.

Additionally or as an alternative to the polyols mentioned above, thepolyol may an acrylate-containing diol or a methacrylate-containingdiol. Examples include:

In some examples, the polyurethane is a water-dispersible acrylicfunctional polyurethane. In some other examples, polyurethane is awater-dispersible (meth)acrylated polyurethane. Suitablewater-dispersible (meth)acrylated polyurethane are commerciallyavailable under the trademarks Ucecoat®6558, Ucecoat®6559, Ebecryl®2002and Ebecryl®2003 (Cytec).

In some examples, the polyurethane dispersions are water-dispersible(meth)acrylated polyurethane, sold under the trade name of NeoRad® R441by NeoResins (Avecia). Other representative but non limiting examples ofsuitable polyurethane dispersions include Ucecoat®7710, Ucecoat®7655(available from Cytec), Neorad®R440, Neorad®R441, Neorade®R447,Neorad®R448 (available from DSM NeoResins), Bayhydrol®UV 2317,Bayhydrol®UV VP LS 2348 (available from Bayer), Lux®430, Lux®399,Lux®484 (available from Alberdingk Boley), Laromer®LR8949,Laromer®LR8983, Laromer® PE22WN, Laromer®PE55WN, Laromer®UA9060(available from BASF).

The amount of polyurethane (solids) dispersed in the primer compositionmay be 0.5 to 40 weight %, for example, 1 to 30 weight %. In someexamples, the amount of polyurethane (solids) in the primer compositionmay be 2 to 25 weight %, for instance, 5 to 15 weight %. As the primercomposition may be applied by analogues, the polyurethane content may berelatively high as jettability may not be a concern. The polyurethanecontent (solids) of the primer composition may be greater than thepolyurethane content (solids) of the ink composition.

The binder composition may be formed using a pre-formed or commerciallyavailable polyurethane dispersion comprising polyurethane dispersed inits own solvent (e.g. water). The amount of polyurethane dispersion usedto form the primer composition may be 5 to 30 weight % of the totalweight of the primer composition.

Any suitable surfactant may be present in the primer composition. Wherethe inkjet ink composition also includes a surfactant, the surfactantpresent in the primer may be the same or different from the surfactantin the inkjet ink composition.

Suitable surfactants may include non-ionic, cationic, and/or anionicsurfactants. Examples include a silicone-free alkoxylated alcoholsurfactant such as, for example, TEGO® Wet 510 (Evonik Tego Chemie GmbH)and/or a self-emulsifiable wetting agent based on acetylenic diolchemistry, such as, for example, SURFYNOL® SE-F (Air Products andChemicals, Inc.). Other suitable commercially available surfactantsinclude SURFYNOL® 465 (ethoxylated acetylenic diol), SURFYNOL® CT 211(non-ionic, alkylphenylethoxylate and solvent free), and SURFYNOL® 104(non-ionic wetting agent based on acetylenic diol chemistry), (all ofwhich are from Air Products and Chemicals, Inc.); ZONYL® FSO (a.k.a.CAPSTONE®, which is a water-soluble, ethoxylated non-ionicfluorosurfactant from Dupont); TERGITOL™ TMN-3 and TERGITOL™ TMN-6 (bothof which are branched secondary alcohol ethoxylate, non-ionicsurfactants), and TERGITOL™ 15-S-3, TERGITOL™ 15-S-5, and TERGITOL™15-S-7 (each of which is a secondary alcohol ethoxylate, non-ionicsurfactant) (all of the TERGITOL™ surfactants are available from The DowChemical Co.). Fluorosurfactants may also be employed.

When present, the surfactant present in the primer composition in anamount ranging from about 0.01 wt % to about 5 wt % based on the totalwt % of the primer composition.

The primer composition may contain less than 0.01 wt % colorant, forexample, less than 0.001 wt % colorant. The primer composition may besubstantially free from colorant. In some examples, the primercomposition may be substantially free from pigment.

The primer composition may be made in-situ just before being applied tothe substrate.

The primer composition may be transparent.

Inkjet Ink Composition

The inkjet ink composition comprises water, a colorant, a photoinitiatorand a curable polyurethane dispersion. The inkjet ink composition mayadditionally comprise a surfactant.

Water may be present in the inkjet ink composition in an amount of atleast 30 weight %, for example, at least 40 or 50 weight %. In someexamples, water may be present in the primer composition in an amount ofat least 60 weight %. Water may be present in an amount of at most 99weight %, for example, at most 95 weight %. In some examples, water maybe present in the inkjet ink composition in an amount of 30 to 99 weight%, for instance, 40 to 98 weight % or 50 to 95 weight %. In otherexamples, water may be present in an amount of 60 to 93 weight %, forinstance, 70 to 90 weight %.

Any suitable colorant may be used in the inkjet ink composition. Thecolorant may be a pigment or a dye. In some examples, the colorant canbe present in an amount from about 0.5 wt % to about 15 wt % based on atotal wt % of the inkjet ink composition. In one example, the colorantcan be present in an amount from about 1 wt % to about 10 wt %. Inanother example, the colorant can be present in an amount from about 5wt % to about 10 wt %.

In other examples, the colorant may be a pigment or dye. In someexamples, the colorant may be a pigment. As used herein, “pigment”generally includes organic or inorganic pigment colorants, magneticparticles, aluminas, silicas, and/or other ceramics, organo-metallics orother opaque particles, whether or not such particulates impart color.Thus, although the present description primarily illustrates the use ofpigment colorants, the term “pigment” can be used more generally todescribe pigment colorants, as well as other pigments such asorganometallics, ferrites, ceramics, etc.

Suitable pigments include the following, which are available from BASFCorp.: PALIOGEN® Orange, HELIOGEN® Blue L 6901F, HELIOGEN® Blue NBD7010, HELIOGEN® Blue K 7090, HELIOGEN® Blue L 7101F, PALIOGEN® Blue L6470, HELIOGEN® Green K 8683, HELIOGEN® Green L 9140, CHROMOPHTAL®Yellow 3G, CHROMOPHTAL® Yellow GR, CHROMOPHTAL® Yellow 8G, IGRAZIN®Yellow 5GT, and IGRALITE® Rubine 4BL. The following pigments areavailable from Degussa Corp.: Color Black FWI, Color Black FW2, ColorBlack FW2V, Color Black 18, Color Black, FW200, Color Black 5150, ColorBlack S160, and Color Black 5170. The following black pigments areavailable from Cabot Corp.: REGAL® 400R, REGAL® 330R, REGAL® 660R,MOGUL® L, BLACK PEARLS® L, MONARCH® 1400, MONARCH® 1300, MONARCH® 1100,MONARCH® 1000, MONARCH® 900, MONARCH® 880, MONARCH® 800, and MONARCH®700. The following pigments are available from Orion Engineered CarbonsGMBH: PRINTEX® U, PRINTEX® V, PRINTEX® 140U, PRINTEX® 140V, PRINTEX® 35,Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW1, Color Black FW 18, Color Black S 160, Color Black S 170, SpecialBlack 6, Special Black 5, Special Black 4A, and Special Black 4. Thefollowing pigment is available from DuPont: TI-PURE® R-101. Thefollowing pigments are available from Heubach: MONASTRAL® Magenta,MONASTRAL® Scarlet, MONASTRAL® Violet R, MONASTRAL® Red B, andMONASTRAL® Violet Maroon B. The following pigments are available fromClariant: DALAMAR® Yellow YT-858-D, Permanent Yellow GR, PermanentYellow G, Permanent Yellow DHG, Permanent Yellow NCG-71, PermanentYellow GG, Hansa Yellow RA, Hansa Brilliant Yellow 5GX-02, HansaYellow-X, NOVOPERM® Yellow HR, NOVOPERM® Yellow FGL, Hansa BrilliantYellow 10GX, Permanent Yellow G3R-01, HOSTAPERM® Yellow H4G, HOSTAPERM®Yellow H3G, HOSTAPERM® Orange GR, HOSTAPERM® Scarlet GO, and PermanentRubine F6B. The following pigments are available from Sun Chemical:QUINDO® Magenta, INDOFAST® Brilliant Scarlet, QUINDO® Red R6700, QUINDO®Red R6713, INDOFAST® Violet, L74-1357 Yellow, L75-1331 Yellow, L75-2577Yellow, and LHD9303 Black. The following pigments are available fromBirla Carbon: RAVEN® 7000, RAVEN® 5750, RAVEN® 5250, RAVEN® 5000 Ultra®II, RAVEN® 2000, RAVEN® 1500, RAVEN® 1250, RAVEN® 1200, RAVEN® 1190Ultra®. RAVEN@ 1170, RAVEN® 1255, RAVEN® 1080, and RAVEN® 1060. Thefollowing pigments are available from Mitsubishi Chemical Corp.: No. 25,No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300, MCF-88, MA600, MA7,MA8, and MA100. The colorant may be a white pigment, such as titaniumdioxide, or other inorganic pigments such as zinc oxide and iron oxide.

Specific examples of a cyan colour pigment may include C.I. PigmentBlue-1, -2, -3, -15, -15:1, -15:2, -15:3, -15:4, -16, -22, and -60.

Specific examples of a magenta colour pigment may include C.I. PigmentRed-5, -7, -12, -48, -48:1, -57, -112, -122, -123, -146, -168, -177,-184, -202, and C.I. Pigment Violet-19.

Specific examples of a yellow pigment may include C.I. Pigment Yellow-1,-2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98,-114, -128, -129, -138, -151, -154, and -180. While several exampleshave been given herein, it is to be understood that any other pigment ordye can be used that is useful in modifying the colour of the UV curableink.

Specific examples of black pigment include carbon black pigments. Anexample of an organic black pigment includes aniline black, such as C.I.Pigment Black 1.

In some examples, the pigment may be a cyan, magenta, black or yellowpigment.

It has been found that certain colorants e.g. black colorants can bestrong absorbers of radiation (e.g. UV radiation). As a result they canbe more difficult to cure. The amount of polyurethane in the inkjet inkcomposition and/or the primer composition may be varied depending on thenature of the colorant, for example, to ensure adequate curing and printdurability.

Any suitable photoinitiator may be employed. The photoinitiator may bepresent in the inkjet ink composition in an amount ranging from about0.1 wt % to about 10 wt % based on a total wt % of the inkjet inkcomposition.

The photoinitiator may be the same or different from the photoinitiatoremployed in the inkjet ink composition. Suitable photoinitiators aredescribed in relation to the primer composition above. However, in someexamples, a water-soluble photoinitiator described in relation to theinkjet ink composition may be used.

The water soluble photoinitiator may be atrimethylbenzoylphenylphosphinic acid metal salt (i.e., TPA salt) havinga formula (I) of:

where n is any integer from 1 to 5 and M is a metal with a valence from1 to 5. Examples of suitable metals include Li, Na, K, Cs, Rb, Be, Mg,Ca, Ba, Al, Ge, Sn, Pb, As, and Sb.

The TPA salt may be formed from ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L) and a metal salt. The ethyl(2,4,6-trimethylbenzoyl) phenylphosphinate may be added to a suitablesolvent (e.g., methyl ethyl ketone (MEK)) to form a solution, and thenthe metal salt may be added to the solution. The solution may be heatedand stirred at a predetermined temperature for a predetermined time toallow the reaction to take place. As a result of the reaction, a solidTPA salt may form. This salt may be collected, washed, and dried.

Two example synthetic pathways for forming a lithium TPA salt (TPA-Li)and a sodium TPA salt (TPA-Na) are shown in the schemes below:

The solubility of the water soluble photoinitiator disclosed herein maybe high. In one example, the water soluble photoinitiator can have awater solubility of at least 0.1 wt %. When the water solubility is atleast 0.1 wt %, it means that of the total wt % of the water solublephotoinitiator added to water, at least 0.1 wt % of the total is watersoluble. In some instances, the water soluble photoinitiator may have awater solubility of at least 0.5 wt %. In some instances, the watersoluble photoinitiator may have a water solubility up to about 20 wt %.

The water soluble photoinitiator may be used in combination with asensitizer. The sensitizer may be a water soluble polymeric sensitizerthat includes a functionalized anthrone moiety, a polyether chain, andan amide linkage or an ether linkage attaching one end of the polyetherchain to the functionalized anthrone moiety. The anthrone moiety may bea thioxanthrenone moiety.

In one example, the polymeric sensitizer may have the formula (Q):

where R₁, R₂, R₃, R₄, and R₅ are each independently selected from thegroup consisting of a hydrogen atom, a substituted or unsubstitutedalkyl group, a substituted or unsubstituted allyl group, a substitutedor unsubstituted alkene or alkenyl group, a substituted or unsubstitutedaryl group, a substituted or unsubstituted aralkyl group, a halogenatom, —NO₂, —O—R_(d), —CO—R_(d), —CO—O—R_(d), —O—CO—R_(d),—CO—NR_(d)R_(e), —NR_(d)R_(e), —NR_(d)—CO—R_(e), —NR_(d)—CO—O—R_(e),—NR_(d)—CO—NR_(e)R_(f), —SR_(d), —SO—R_(d), —SO₂—R_(d), —SO₂—O—R_(d),—SO₂NR_(d)R_(e) and a perfluoroalkyl group. R_(d), R_(e), and R_(f) areeach independently selected from the group consisting of a hydrogenatom, a substituted or unsubstituted alkyl group, a substituted orunsubstituted allyl group, a substituted or unsubstituted alkene oralkenyl group, a substituted or unsubstituted aryl group, and asubstituted or unsubstituted aralkyl group. Some examples of suitablealkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,pentyl, hexyl, etc. One example of a suitable alkene group is anethylene group. Some examples of suitable aryl groups include phenyl,phenylmethyl, etc. In formula Q above, X is O, S, or NH and thepolyether chain has n number of repeating monomer units, where n rangesfrom 1 to 200. As shown in formula Q above, the linkage is an etherlinkage.

When present, the sensitizer may be present in an amount of 0.1 wt % toabout 10 wt % of the inkjet ink composition.

Any suitable curable polyurethane dispersion may be used to form theinkjet ink composition. For example, a pre-formed curable polyurethanedispersion may be added to the remaining ink components. Such apre-formed curable polyurethane dispersion may comprise polyurethanedispersed in its own solvent (e.g. water). The curable polyurethanedispersion may be present in the inkjet ink composition in an amount of0.5 to 20 weight % or 2 to 15 weight %, for example, 3 to 12 weight %.

The curable polyurethane (solids) that is dispersed in an inkjet inkcomposition may be present in the inkjet ink composition an amount of0.1 to 30 weight % or 0.1 to 20 weight %. In some instances, the curablepolyurethane (solids) that is dispersed in an inkjet ink composition maybe present in an amount of 0.1 to 10 weight %, for example, 0.5 to 7weight %, or 0.6 to 5 weight % of the total weight of the inkjet inkcomposition.

Suitable curable polyurethanes are described in relation to the primercomposition above. The curable polyurethane in the inkjet inkcomposition may be the same or different from the curable polyurethanein the primer composition. In some examples, the curable polyurethane isa pH stable polyurethane. pH stable polyurethane may form pH stablepolyurethane dispersions that may be resistant to hydrolysis. In someexamples, the pH of the pH stable polyurethane dispersions may remainsubstantially stable when the dispersions are stored for a period oftime. Thus, inkjet inks formed using such pH stable polyurethanes mayhave a longer shelf-life, as the tendency for pigments dispersed in theinkjet ink composition to crash out of the inkjet ink composition may bereduced.

The pH stable polyurethane may comprise a polyurethane polymercomprising a polyurethane backbone having at least one terminal (orcapping) group selected an acrylamide-containing group, astyrene-containing group, an allyl-containing group:

For avoidance of doubt the CAPS and CHES terminal groups above may be inanionic form, namely:

Where the terminal group is selected from CAPS or CHES, these cappinggroups (CAPS) and (CHES) may be formed by reacting a polyurethanepre-polymer with 3-(cyclohexylamino)-1-propanesulfonic acid and/or2-(cyclohexylamino)ethanesulfonic acid. The3-(cyclohexylamino)-1-propanesulfonic acid and2-(cyclohexylamino)ethanesulfonic acid may react with terminal —N═C═Ogroups on the polyurethane pre-polymer. These capping groups may help tostabilise the polyurethane dispersion.

Where the terminal or capping group is an acrylamide, theacrylamide-containing capping group may be CH₂═CHC(O)NH(CH₂)_(n)O—,wherein n is an integer from 1 to 10. In some examples, n is 1 to 6, forinstance, 1 to 4 or 2 to 3. In one example, the acrylamide-containingcapping group may be a group of the formula below:

The acrylamide-containing group may be formed by reacting a polyurethanepre-polymer with an acrylamide-containing monoalcohol or monoamine. Forexample, an acrylamide-containing monoalcohol may react with terminal—N═C═O groups on the polyurethane pre-polymer. An example of a suitableacrylamide-containing mono-alcohol may be:

Where the capping group comprises a styrene-containing group, suitablestyrene-containing capping groups may include:

Styrene-containing groups (e.g. Groups (II) to (VI) above) may be formedby reacting suitable styrene-containing mono-alcohols or monoamines witha polyurethane pre-polymer. For example, the styrene-containingmonoalcohol may react with terminal —N═C═O groups on the polyurethanepre-polymer. The styrene-containing mono-alcohols corresponding toGroups (II) to (VI) may be:

Where the capping group comprises an allyl-containing group, theallyl-containing group may comprise an allyl ether group or an allylamine group. Suitable allyl-containing capping groups include:

The allyl-containing groups (e.g. Groups (VII) to (XIII) above) may beformed by reacting suitable allyl-containing mono-alcohols or monoamineswith a polyurethane pre-polymer. For example, the allyl-containingmonoalcohol or monoamine may react with terminal —N═C═O groups on thepolyurethane pre-polymer. The allyl-containing mono-alcohols ormonoamines corresponding to Groups (VII) to (XIII) above may be:

In one example, the polyurethane dispersion may comprise polyurethanepolymers that comprise polyurethane backbones having terminal groupsselected from acrylamide-containing groups, styrene-containing groups,and allyl-containing groups. The dispersion may be devoid ofpolyurethane polymers that comprise polyurethane backbones havingterminal methacrylate-containing or acrylate-containing groups.

In one example, the polyurethane dispersion may comprise at least onepolyurethane polymer comprising a polyurethane backbone having at leastone terminal (or capping) group selected from an acrylamide-containinggroup, a styrene-containing group, an acrylate-containing group, amethacrylic-containing group and an allyl-containing group, and at leastone polyurethane polymer comprising a polyurethane backbone having atleast one terminal (or capping) ionic group; and/or at least onepolyurethane polymer comprising a polyurethane backbone that is cappedat one end with a terminal (or capping) group selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group and at the opposite end with a terminal ionicgroup.

In the polyurethane that is dispersed in the ink or primer composition,1 to 99 weight % of the capping groups may be ionic groups, while 99 to1 weight % of the capping groups may be selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group. In some examples, 5 to 70 weight % of thecapping groups may be ionic groups, while 95 to 30 weight % of thecapping groups may be selected from an acrylamide-containing group, astyrene-containing group, an acrylate-containing group, amethacrylic-containing group and an allyl-containing group. In someexamples, 10 to 50 weight % of the capping groups may be ionic groups,while 90 to 50 weight % of the capping groups may be selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group. In other examples, 20 to 40 weight % of thecapping groups may be ionic groups, while 80 to 60 weight % of thecapping groups may be selected from an acrylamide-containing group, astyrene-containing group, an acrylate-containing group, amethacrylic-containing group and an allyl-containing group.

In one example, the polyurethane dispersion may comprise at least onepolyurethane polymer comprising a polyurethane backbone that is cappedat one end with a terminal (or capping) group selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group and capped at the opposite end with a terminalionic group.

In one example, the polyurethane dispersion may comprise (i) at leastone polyurethane polymer comprising a polyurethane backbone that iscapped at one end with a terminal (or capping) group selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group and capped at the opposite end with a terminalionic group; and (ii) at least one polyurethane polymer comprising apolyurethane backbone that is capped at both ends with a terminal (orcapping) group selected from an acrylamide-containing group, astyrene-containing group, an acrylate-containing group, amethacrylic-containing group and an allyl-containing group or (iii) atleast one polyurethane polymer comprising at least one polyurethanepolymer comprising a polyurethane backbone that is capped at both endswith ionic groups.

In one example, the polyurethane dispersion may comprise (i) at leastone polyurethane polymer comprising a polyurethane backbone that iscapped at one end with a terminal (or capping) group selected from anacrylamide-containing group, a styrene-containing group, anacrylate-containing group, a methacrylic-containing group and anallyl-containing group and capped at the opposite end with a terminalionic group; (ii) at least one polyurethane polymer comprising apolyurethane backbone that is capped at both ends with a terminal (orcapping) group selected from an acrylamide-containing group, astyrene-containing group, an acrylate-containing group, amethacrylic-containing group and an allyl-containing group and (iii) atleast one polyurethane polymer comprising at least one polyurethanepolymer comprising a polyurethane backbone that is capped at both endswith ionic groups.

The ionic group may contain a carboxylate group, carboxylic acid group,sulphonate and/or a sulphonic acid group. The ionic group may be formedby reacting an amino carboxylic acid or an amino sulphonic with apolyurethane pre-polymer, for example, with terminal —N═C═O groups onthe polyurethane pre-polymer. Suitable amino sulphonic acids includetaurine, CAPS or CHES (see above). The ionic groups may help to keep thepolyurethane particles in dispersion in water.

In one example, the polyurethane dispersion may comprise at least onepolyurethane polymer comprising a polyurethane backbone having at leastone terminal (or capping) group selected from a methacrylic-containinggroup and/or an acrylate-containing group, and at least one polyurethanepolymer comprising a polyurethane backbone having at least one terminal(or capping) ionic group selected from

and/or at least one polyurethane polymer comprising a polyurethanebackbone that is capped at one end with a terminal (or capping) groupselected from a methacrylic-containing group and/or anacrylate-containing group, and at the opposite end with a terminal groupselected from CAPS or CHES above. In the polyurethane that is dispersedin the ink or primer composition 1 to 99 weight % of the capping groupsmay be CAPS and/or CHES, while 99 to 1 weight % of the capping groupsmay be selected from an acrylate-containing group and/or amethacrylic-containing group. In some examples, 5 to 70 weight % of thecapping groups may be CAPS and/or CHES, while 95 to 30 weight % of thecapping groups may be selected from an acrylate-containing group and/ora methacrylic-containing group. In some examples, 10 to 50 weight % ofthe capping groups may be CAPS and/or CHES, while 90 to 50 weight % ofthe capping groups may be selected from an acrylate-containing groupand/or a methacrylic-containing group. In some examples, 20 to 40 weight% of the capping groups may be CAPS and/or CHES, while 80 to 60 weight %of the capping groups may be selected from an acrylate-containing groupand/or a methacrylic-containing group.

In one example, the polyurethane dispersion may comprise at least onepolyurethane polymer comprising a polyurethane backbone that is cappedat one end with a terminal (or capping) group selected from anacrylate-containing group and/or a methacrylic-containing group andcapped at the opposite end with a terminal CAPS or CHES group.

In one example, the polyurethane dispersion may comprise (i) at leastone polyurethane polymer comprising a polyurethane backbone that iscapped at one end with a terminal (or capping) group selected from anacrylate-containing group and/or a methacrylic-containing group, andcapped at the opposite end with a terminal CAPS or CHES group; and (ii)at least one polyurethane polymer comprising a polyurethane backbonethat is capped at both ends with a terminal (or capping) group selectedfrom an an acrylate-containing group and/or a methacrylic-containinggroup or (iii) at least one polyurethane polymer comprising at least onepolyurethane polymer comprising a polyurethane backbone that is cappedat both ends with terminal groups selected from CAPS and/or CHES groups.

In one example, the polyurethane dispersion may comprise (i) at leastone polyurethane polymer comprising a polyurethane backbone that iscapped at one end with a terminal (or capping) group selected from anacrylate-containing group and/or a methacrylic-containing group andcapped at the opposite end with a terminal CAPS or CHES group; (ii) atleast one polyurethane polymer comprising a polyurethane backbone thatis capped at both ends with a terminal (or capping) group selected froman acrylate-containing group and/or a methacrylic-containing group and(iii) at least one polyurethane polymer comprising at least onepolyurethane polymer comprising a polyurethane backbone that is cappedat both ends with terminal groups selected from CAPS and/or CHES groups.

Suitable acrylate- or methacrylate-containing capping groups may include

Groups (XIII) to (XIVI) above may be formed by reacting thecorresponding methacrylate/acrylate-containing mono-alcohols with apolyurethane pre-polymer, for example, with —N═C═O terminal groups onthe pre-polymer.

The polyurethane backbone of the polyurethane polymers present in the pHstable polyurethane dispersion may be formed from the reaction between areactive diol and a diisocyanate. The reactive diol may be selected froman acrylate-containing diol, a methacrylate-containing diol, andcombinations thereof. Where the capping unit comprises anacrylamide-containing group, the reactive diol may be selected from anacrylate-containing diol, a methacrylate-containing diol and anacrylamide-containing diol. Where the capping unit comprises astyrene-containing group, the reactive diol may be selected from anacrylate-containing diol, a methacrylate-containing diol astyrene-containing diol. Where the capping unit comprises anallyl-containing group, the reactive diol may be selected from anacrylate-containing diol, a methacrylate-containing diol and anallyl-containing diol.

Suitable methacrylate-containing and acrylate-containing reactive diolsinclude:

The reactive diol, may also be a styrene-containing reactive diolselected from:

The reactive diol may also be an allyl-containing containing diolselected from:

Suitable diisocyanates include methylene diphenyl diisocyanate,hexamethylene diisocyanate, p-tetramethyl xylene diisocyanate,m-tetramethyl xylene diisocyanate, bitolylene diisocyanate, toluenediisocyanate, 4,4′-Methylene dicyclohexyl diisocyanate, p-phenylenediisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate,trimethylhexamethylene diisocyanate and mixtures thereof.

In one example, the diisocyanate is selected from at least one of 2,2,4-trimethyl hexamethylene diisocyanate, isophorone diisocyanate,hexamethylene diisocyanate, methylene diphenyl diisocyanate and4,4′-Methylene dicyclohexyl diisocyanate.

A blend of two diisocyanates may be used.

For example, the diisocyanates may be a blend of 4,4′-Methylenedicyclohexyl diisocyanate and hexamethylene diisocyanate

In one example, a blend of at least two diisocyanates is reacted with areactive diol to produce the polyurethane backbone. The reactive diolmay be a methacrylate-containing and/or acrylate-containing reactivediol. In some examples, the reactive diol may be anacrylamide-containing reactive diol, an allyl-containing reactive dioland/or a styrene-containing reactive diol. In one example, the reactivediol may be a methacrylate-containing or acrylate-containing diol thatis bisphenol A-free. As shown above, examples of such diols include:

The polyurethane backbone may be devoid of any ionic side groups, forexample, acid stabilisation groups (e.g. carboxylic or sulphonic acidgroups). Such ionic groups may act as capping groups at the terminalend(s) of at least some of the polyurethane polymer strands in thepolyurethane dispersion.

In one example, the polyurethane dispersion is formed by reacting areactive diol with a diisocyanate to form a polyurethane pre-polymer. Apolymerisation initiator may be used to initiate polymerisation. TheNCO/OH ratio may range from greater to 1 to 8, for example, 1.2 to 5.

The polymerisation may be carried out to produce a polyurethanepre-polymer. Once the polyurethane pre-polymer is formed, a cappingagent may be added to the reaction mixture. For example, the cappingagent may be a monoalcohol or monoamine selected from amethacrylate-containing monoalcohol, an acrylate-containing monoalcohol,a acrylamide-containing monoalcohol, a styrene-containing monoalcohol,an allyl-containing monoalcohol or an allyl-containing monoamine. Themonoalcohol or monoamine may react with terminal —N═C═O groups on thepolyurethane pre-polymer to cap the polyurethane pre-polymer. Thereaction is carried out such that at least some of the polyurethanepre-polymer strands are capped by this reaction. In some examples, mostof the polyurethane pre-polymer strands are capped by this reaction. Forexample, at least 10% of unreacted —N═C═O groups are capped by thisreaction. In some instances, 60 to 90%, for instance, 65 to 85% ofunreacted —N═C═O groups are capped by this reaction.

An amino carboxylic acid or an amino sulphonic acid may then be added tothe reaction mixture. As mentioned above, suitable acids includetaurine, 3-(cyclohexylamino)-1-propanesulfonic acid and2-(cyclohexylamino)ethanesulfonic acid. The amino carboxylic acid oramino sulphonic acid may react with the remaining —N═C═O groups. Thesegroups form can form ionic capping groups that help to stabilise thedispersion of polyurethane in e.g. water.

The pH stable curable polyurethane may have an acid number of 20 to 100.The pH stable curable polyurethane may have a double bond density from1.5 to 1.0 meq/g.

The particle size range of the pH stable polyurethane dispersion may be20 to 200 nm.

Any suitable surfactant may be present in the inkjet ink composition.Suitable surfactants are described in relation to the primer compositionabove. The surfactant employed in the inkjet ink composition may be thesame or different from the surfactant used in the primer composition.When present, the surfactant present in the inkjet ink composition in anamount ranging from about 0.01 wt % to about 5 wt % based on the totalwt % of the inkjet ink composition.

The inkjet ink composition may include a co-solvent in addition towater. Classes of co-solvents that may be used can include organicco-solvents, including alcohols (e.g., aliphatic alcohols, aromaticalcohols, polyhydric alcohols (e.g., diols), polyhydric alcoholderivatives, long chain alcohols, etc.), glycol ethers, polyglycolethers, a nitrogen-containing solvent (e.g., pyrrolidinones,caprolactams, formamides, acetamides, etc.), and a sulfur-containingsolvent. Examples of such compounds include primary aliphatic alcohols,secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols,ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higherhomologs (C6-C12) of polyethylene glycol alkyl ethers, N-alkylcaprolactams, unsubstituted caprolactams, both substituted andunsubstituted formamides, both substituted and unsubstituted acetamides,and the like. Still other examples of suitable co-solvents includepropylene carbonate and ethylene carbonate.

A single co-solvent may be used, or several co-solvents may be used incombination. When included, the co-solvent(s) is/are present in total inan amount ranging from 0 wt % to 60 wt %, depending on the jettingarchitecture, though amounts outside of this range can also be used. Asother example, the co-solvent(s) may range from about 1 wt % to about 30wt % or about 20 wt % of the total wt % of the inkjet ink composition.

The inkjet ink composition may also include various other additives toenhance the properties of the ink composition for specific applications.Examples of these additives include those added to inhibit the growth ofmicroorganisms, viscosity modifiers, materials for pH adjustment,sequestering agents, anti-kogation agents, preservatives, and the like.Such additives may be present in an amount of 0 to 5 wt % of the inkjetink composition.

Printing Process

As described above, the present disclosure provides an inkjet printingprocess that comprises applying a radiation-curable primer compositiononto a substrate. The primer may be applied using any suitabletechnique. For example, the primer may be applied by brush, roller,knife, spraying or inkjet ink printing. The primer may be applied toform a primer layer that is 0.1 to 5 microns thick, for example, 0.5 to4 microns thick or 1 to 3 microns thick.

Prior to application of the primer, the substrate may be treated, forexample, with corona treatment.

Once the primer is applied, it may be dried. The inkjet ink compositionmay be inkjet printed over the primer layer. Any suitable inkjet inkprinting method may be used. Examples include thermal and piezoelectricinkjet printing. In some examples, thermal inkjet printing is employed.

In some examples, a fixer may be applied to the primer layer prior tothe inkjet ink composition. The fixer may help to optimise thedeposition of pigment onto the print substrate. The fixer may help tooptimise the deposition of pigment onto the print substrate. Suitablefixers may include one or more calcium salts and water. Examples ofsuitable calcium salts include calcium nitrate tetrahydrate and calciumpropionate. In one example, the fixer comprises calcium nitratetetrahydrate and calcium propionate. Surfactant may also be present inthe fixer composition. A suitable surfactant may be a non-ionicsurfactant, for example, Surfonyl® SEF. The fixer may also include abiocide. A suitable biocide may be Acticide® B20. Water may be presentin the fixer in an amount of 5 to 30 weight % of the fixer composition.The fixer may be applied after the substrate has been treated by coronatreatment. In some examples, the fixer may be applied to a substratethat has not been corona treated.

Once the inkjet ink is printed on the substrate it may be cured.

Any suitable source of radiation may be used to cure the inkjet ink andprimer. In one example, UV radiation is employed. Suitable sources of UVradiation include UV lamps, LED (light emitting diode) lamps, LEP (lightemitting plasma) plasma torches, or lasers operating in the UV range.

The actual wavelength (within the UV range of 280 nm to 400 nm) andintensity of the ultraviolet radiation used may vary, depending at leastin part, upon the curable polyurethane in the binder and inkjet inkcomposition. Examples of suitable UV LED wavelengths include 365 nm, 385nm, 395 nm or 405 nm, for example, 365 nm and 395 nm.

The printing process of the present disclosure can be used to print on abroad selection of substrates, including untreated plastics, flexible aswell as rigid, porous or non-porous substrates. Some examples includepaper (e.g., plain paper, coated, glossy paper, etc.), cardboard, foamboard, textile, and plastics. Examples of suitable plastic substratesinclude vinyl substrates, for example, vinyl graphic films availablefrom 3M™ under the trademark Scotchcal™ series IJ-40. Other examplesinclude acrylic substrates, for example, acrylic cast graphic filmsavailable from 3M™ under the trademark Controltac™ (e.g. 180-10(cast)).Other examples include acrylic glass substrates (PMMA), polypropylenesubstrates, polystyrene substrates (e.g. high impact polystyrenesubstrates), PVC substrates and polycarbonate substrates.

FIG. 1 depicts schematically, by way of example only, an example of thesequence of steps that may be taken to perform an example inkjetprinting process of the present disclosure. As can be seen from theFIGURE, primer 10 may be applied to a print substrate 12. The primerlayer on the substrate 12 may then be dried 14. A fixer 16 may then bedeposited onto the primer layer and an ink jet ink composition 18 inkjetprinted over the fixer. The printed ink layer may be dried by a dryer20. The printed ink layer may be cured by exposing the primer and inklayers to UV-LED 22.

To further illustrate the present disclosure, examples are given below.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

EXAMPLES Example 1—Synthesis of Curable pH Stable Acrylamide-Based PUD

38.884 g of g of BGDA (see compound XVII above), 0.389 g of4-methoxyphenol (MEHQ), 42.103 g of 4,4′-Methylene dicyclohexyldiisocyanate (H12MDI), and 42 g of acetone were mixed in a 500 ml of4-neck round bottom flask. A mechanical stirrer with glass rod andTeflon blade was attached. A condenser was attached. The flask wasimmersed in a constant temperature bath at 60° C. The system was keptdry. 3 drops of DBTDL was added to initiate the polymerization.Polymerization was continued for 3 hrs at 60° C. 0.5 g samples waswithdrawn for % NCO titration to confirm the reaction. The measured NCOvalue was 7.6%. Theoretical % NCO should be 8.32%. 12.318 g of HEAA(N-hydroxylethyl acrylamide, CAS #7646-67-5, purchased from SigmaAldrich), 0.159 g of MEHQ, and 19 g of acetone were mixed in a beakerand added to the reactor over 30 sec. 9 g of acetone was used to rinseoff the residual monomers on the beaker and added to the reactor. Thepolymerization was continued 3 hours at 50° C. 0.5 g of pre-polymer waswithdrawn for final % NCO titration. The measured NCO value was 2.41%.The theoretical % NCO should be 2.41%. The polymerization temperaturewas reduced to 40° C. 6.695 g of taurine, 4.494 g of 50% NaOH, and33.474 g of deionized water are mixed in a beaker until taurine iscompletely dissolved. Taurine solution was added to the pre-polymersolution at 40° C. with vigorous stirring over 1-3 mins. The solutionbecame viscous and slight hazy. Stirring was continued for 30 mins at40° C. The mixture became clear and viscous after 15-20 mins at 40° C.194.649 g of cold deionized water was added to polymer mixture in 4-neckround bottom flask over 1-3 mins with good agitation to formpolyurethane dispersion (PUD). The agitation was continued for 60 minsat 40° C. The PUD dispersion was filtered through 400 mesh stainlesssieve. Acetone was removed with rotorvap at 50° C. (add 2 drops (20 mg)BYK®-011 de-foaming agent If there are a lot of foaming). The final PUDdispersion was filtered through fiber glass filter paper. Particle sizemeasured by Malvern Zetasizer is 26.8 nm. Its pH was 6.0. Solid contentwas 30.04%. This PUD shows less than 0.4 unit pH drop after 1 week underaccelerated shelf life testing (ASL, storage at 60 degrees C.).

Example 2

The curable pH stable PUD produced in Example 1 was used to formulate aninkjet ink formulation.

Component Weight % Surfactant (Surfonyl ® CT-211, supplied 0.80 byAirProducts ®) Dynax ® DX-4000 (fluorsurfactant, 0.50 supplied byDynax ®) Water soluble photoinitiator (TPA Na) 0.50 Water solublesensitizer² 0.25 curable PUD of Example 1 3-12.00¹ Black or Magentapigment 2.5 or 3.75, respectively Water Balance ¹0.9 to 3.6 weight %polyurethane (solids) dispersed in ink composition; ²A photosensitizerbased on a functionalized anthrone molety coupled to a polyether chain,see Q above

Example 3

A curable primer composition was prepared having the followingcomposition: 35% polyurethane dispersion (Ucecoat® 7571 from Allnex®),3% surfactant (Tegowet® 510) and 0.3% photo initiator (Irgacure®,commercially available from BASF Corp. 819DW).

Example 4

In this example, 3 gsm of a coated paper substrate (Graph+®) was coatedwith the primer composition of Example 3. The primed substrate was thenprinted with an inkjet ink composition of Example 2 (magenta) using athermal inkjet printer. The print speed was 100 ft/min. The printedsubstrate was then dried and cured using UV-LED at 395 nm.

The cured substrates were subjected to a heated Sutherland rub test (177degrees C. (350 degrees F.), 27.6 kPa (4 psi) heated weight, speed 2, 10cycles) and smear durability test (4 in. length, 1700 g weight,Mellotex). For the Sutherland rub test, the tested substrates wereinspected by visual inspection. A score of 5 (best) was indicative ofexcellent rub resistance, while a score of 0 (worst) was indicative ofpoor rub resistance.

The results are shown in Table 1 below. Smear durabilities of 237 to 238were considered to be good. The heated Sutherland rub was excellent evenat low amount of polyurethane dispersion.

TABLE 1 wt % of curable PUD of Example 1 in ink tested/ (wt % Heatedpolyurethane Sutherland solids in ink Optical 75° Rub Smear tested)Density Gloss Test Mean 3 (0.9) 1.72 99 5 237.5 6 (1.8) 1.64 98 5 238.49 (2.7) 1.63 99 5 237.8 12 (3.6)  1.57 96 5 237.8

Example 5

The procedure of Example 4 repeated except that a fixer was applied tothe primed substrate prior to inkjet printing of the ink composition. Inthis Example, magenta and black inks were used with varying amounts ofthe curable PUD of Example 1 as shown in Table 2 below.

In addition to the heated Sutherland rub test and smear durability testsabove, the cured substrates were also subjected to a Quanta regularSutherland rub test (4 lbs, 200 cycles, Mellotex). A score of 5 wasindicative of excellent rub resistance, while a score of 0 wasindicative of poor rub resistance

The results are shown in Table 2 below.

TABLE 2 wt % curable PUD of Example 1 in ink tested/(wt % polyurethaneHot Quanta solids in ink Smear Sutherland Sutherland tested) Colour OD75 Gloss Mean Rub Rub  5 (1.5) Black 2.03 88 236.8 3 1  5 (1.5) Magenta1.76 89 233.8 5 3 10 (3.0) Black 2.37 92 233.9 3 4 10 (3.0) Magenta 1.8690 232.6 5 4

Example 6

In this Example, the procedure of Example 4 was repeated except that thesubstrate was pre-treated by corona treatment prior to application ofthe primer. Corona treatment is used to increase the surface energy ofthe vinyl and improve wetting of the primer. The substrates were sealedin an aluminium envelope until printed with magenta and black inks ofExample 2.

The cured and printed substrates were subjected to an eraser rub test (1Weight (250 g), 10 Cycles), Windex rub (1 Weight (250 g), 5 Cycles,Crockmeter Cloth), IPA rub (1 Weight (250 g), 5 Cycles, CrockmeterCloth) and a quanta regular Sutherland rub tests. The results are shownin Table 3 below. For the Windex rub, IPA rub and eraser rub tests, ascore of 0 (best) is indicative of excellent durability, while a scoreof 5 (worst) is indicative of poor durability. Eraser rub scores of 2and 3 were considered to be acceptable.

TABLE 3 wt % curable PUD of Example 1 in ink tested/(wt % Quantapolyurethane Regular solids in ink 75 Sutherland tested) Colour OD GlossEraser Windex IPA Rub  5 (1.5) Black 1.81 78 2 1.5 5 4  5 (1.5) Magenta1.58 81 3 0.5 1.5 5 10 (3.0) Black 2.15 93 2 0.5 1.5 5 10 (3.0) Magenta1.85 90 2 0.5 1.5 4

Comparative Example 7

As a comparative example, the procedure of Example 6 was repeatedwithout the primer layer.

The cured substrates were tested for Windex rub resistance and IPA rubresistance. The results are shown in Table 4 below.

TABLE 4 wt % curable PUD of Example 1 in ink tested/(wt % polyurethanesolids in ink 75 tested) Colour OD Gloss Windex IPA  5 (1.5) Black 1.5678 4 5  5 (1.5) Magenta 1.42 72 2 3.5 10 (3.0) Black 1.89 86 4 5 10(3.0) Magenta 1.69 77 0.5 3.5

Example 8

Example 5 above was repeated in the absence of the fixer. The resultsare shown in Table 5 below

TABLE 5 wt % curable PUD of Example 1 in ink tested/(wt % polyurethaneHot Quanta solids in ink 75 Smear Sutherland Sutherland tested) ColourOD Gloss Mean Rub Rub  5 (1.5) Black 2.11 98 234.9 1 1  5 (1.5) Magenta1.93 95 232.2 4 3 10 (3.0) Black 2.19 95 238 3 3 10 (3.0) Magenta 1.9692 232.1 4 3

The invention claimed is:
 1. An inkjet printing process comprisingapplying a radiation-curable primer composition onto a substrate to forma primer layer, said radiation-curable primer composition comprising acurable polyurethane dispersion, a photoinitiator, and water, inkjetprinting an inkjet ink composition onto the primer layer as a printedinkjet ink layer, the inkjet ink composition comprising a colorant, acurable polyurethane dispersion, a photoinitiator, and water, wherein anamount of curable polyurethane dispersed in the inkjet ink compositionis 0.1 to 30 weight %, and curing the printed inkjet ink layer on thesubstrate by exposing both the primer layer and printed inkjet ink layeron the substrate to radiation, wherein polyurethane in the primer layerand the curable polyurethane in the printed inkjet ink layer arecrosslinked during curing to form a crosslinked polyurethane network. 2.The process as claimed in claim 1, wherein the primer layer is appliedas an analogue primer.
 3. The process as claimed in claim 1, wherein theprimer layer and the printed inkjet ink layer on the substrate are curedby exposure to UV-LED.
 4. The process as claimed in claim 1, wherein thecurable polyurethane is present in an amount of 0.5 to 5 weight % of theinkjet ink composition.
 5. The process as claimed in claim 1, whereinthe curable dispersion includes a curable polyurethane in an amount of 1to 30 weight % of the radiation-curable primer composition that isapplied to the substrate.
 6. The process as claimed in claim 1, whereinthe curable polyurethane dispersion in the inkjet ink composition is apH stable curable polyurethane dispersion.
 7. The process as claimed inclaim 6, wherein the pH stable curable polyurethane dispersion comprisesa polyurethane polymer including a polyurethane backbone having at leastone terminal group selected from at least one of anacrylamide-containing group, a styrene-containing group, anallyl-containing group,


8. The process as claimed in claim 6, wherein the pH stable curablepolyurethane dispersion comprises a polyurethane polymer including apolyurethane backbone that is capped at one end with a terminal groupselected from at least one of an acrylamide-containing group, astyrene-containing group and an allyl-containing group and at theopposite end with a terminal group comprising a carboxylate, carboxylicacid, sulphonate or sulphonic acid group.
 9. The process as claimed inclaim 6, wherein the pH stable curable polyurethane dispersion comprisespolyurethane polymer including a backbone that is capped at one end witha terminal group selected from an acrylamide-containing group, astyrene-containing group, an allyl-containing group, amethacrylate-containing or acrylate-containing group, and at theopposite end with a terminal group selected from at least one of:


10. The process as claimed in claim 6, wherein pH stable curablepolyurethane dispersion comprises a polyurethane polymer formed from thereaction of a) a blend of at least 2 isocyanates and b) a reactive diol.11. The process as claimed in claim 1, wherein the curable polyurethanein the inkjet ink composition is different than a curable polyurethanein the radiation-curable primer composition.
 12. The process as claimedin claim 1, further comprising drying the primer layer, and applying afixer to dried primer layer prior to the inkjet printing of the inkjetink composition over the fixer.
 13. The process as claimed in claim 1,wherein a concentration of curable polyurethane dispersed in theradiation-curable primer composition is greater than a concentration ofthe curable polyurethane dispersed in the inkjet ink composition.
 14. Aprinted substrate comprising a primer layer disposed on the substrate,an ink layer comprising a colorant disposed over the primer layer, and acrosslinked polyurethane network that surrounds the colorant and extendsfrom the primer layer into the ink layer, wherein polyurethane in theprimer layer and the curable polyurethane in the printed inkjet inklayer are crosslinked during curing such that reactive groups of thepolyurethane in the primer layer crosslink with reactive groups of thepolyurethane in the printed inkjet ink layer.
 15. The process as claimedin claim 1, wherein the photoinitiator in the radiation-curable primercomposition, the inkjet ink composition, or the combination thereof is atrimethylbenzoylphenylphosphinic acid metal salt (i.e., TPA salt) havinga formula of:

wherein n is any integer from 1 to 5, M is a metal selected from Li, Na,K, Cs, Rb, Be, Mg, Ca, Ba, Al, Ge, Sn, Pb, As, or Sb, and n+ is avalence from 1 to 5.